1. Field of the Invention
The present invention relates to private branch telephone exchange systems and, more particularly, to a two-wire exchange system which is responsive to a tone signal from the local telephone instrument for placing the calling party on "hold" and connecting the incoming line to music on hold. The system may also connect the local instrument to an intercom paging system having paging, incoming call waiting, and party-on-hold warning tones.
2. General Background and Prior Art
The telephone and telecommunication industries often employ various paging, signalling, and intercom functions as part of an overall telephone network for use in locations such as offices, hospitals, industrial plants, and the like where incoming calls are distributed from a central keyboard or operator to a plurality of persons each having individual telephone units.
Most of these prior art type telecommunications networks which would perform many of the same signalling, intercom and paging functions, but which could be utilized with simple two wire telephone units since individual two wire telephone instruments are a substantial savings to the company which installs telephones when compared to conventional multi-wire intercom and telephone network systems and their complex electronic components.
It would be desirable to have all of those known conventional functions produced by prior art type telecommunication elements and networks in a simple two wire exchange unit.
Various telecommunication functions such as signalling, intercom, and paging functions would be desirable features useful to the consumer in connection with simple, parallel connected two wire telephone instruments.
Some prior art systems utilize a paging system which receives outside calls on an incoming board provided with a plurality of separate buttons each of which is interfaced with a single telephone instrument as, for example, a central office keyboard having buttons for each individual office or telephone line throughout the system.
Some prior art telecommunication systems or networks utilize a paging or intercom system which places the incoming call on "hold" and supplies music to the distant party while the keyboard operator or receptionist locates the desired recipient of the call. The music can be supplied by nearby am or fm radio stations through the tuner which is known in the art and available on prior art type commercially available telephone systems.
Another desirable feature of telecommunication or intercom systems would be the ability to receive incoming calls while the system is being used to provide an intercom function between separate common connected instruments.
Some prior art type switching systems or intercom systems utilize the technique of switching responsive to certain tones which are generated by the individual phone instruments. In this regard, see U.S. Pat. No. 4,031,329 issued to B. R. Saxton and entitlted "Time Limited Telephone Paging" which employs a relay switch actuated by dual frequency tones. Also, U.S. Pat. No. 4,081,614 issued to James Dahlquist and entitled "Supervised Single Link Telephone System" teaches such switching technique responsive to the generation of dual tones by depressing the asterisk push button at the administrative telephone set.
U.S. Pat. No. 4,100,375 issued to David L. Noller and entitled "Telephone Intercom and Remote Control System" employs a standard telephone instrument having dual tone multifrequency (DTMF) signalling. The telephone hook switch sensing circuit provides a trigger to connect a tone decoder across the talk path for a period of time established by a time delay circuit. When the instrument is tone dialed, the output of the tone decoder is fed respectively to: a gate circuit which switches the telephone instrument from the local intercom battery to an outside telephone line; a "hold" feature circuit which places the outside call on "hold"; a remote control circuit which turns on and off devices remote from the system; or to individual bells or other instruments within the system.
Music on "hold" functions in key telephone systems are seen in U.S. Pat. No. 3,909,553 issued to Richard A. Marshall, and U.S. Pat. No. 4,056,695 issued to Ronald James Angner and James Lacy.
Various other telephone/intercom systems controlled by tone generation are seen in other U.S. patents. For example, in U.S. Pat. No. 3,941,944 issued to Alexander McIntosh, there is provided a signalling device for key telephone systems such as intercom systems. There is taught in that patent a system for decoding the tone output from touch tone telephones, indicating which digit has been operated and selectively signalling the called party.
In U.S. Pat. No. 4,004,106 issued to Gerald Yachabach, et al., there is provided "A Line Circuit for Use with a Key Telephone System." The Yachabach patent provides a system for indicating an incoming call, a call placed on "hold," and an answered call. There is further provided a means for automatically indicating that the incoming call has been placed on "hold" for a pre-determined time period. There is further provided a solid state device which switches telephone instrument lamp current for visual indication of the various line circuit operations.
U.S. Pat. No. 4,037,058 issued to Robert David Stine provides a control circuit including a mechanical interrupter which provides a plurality of interrupted ringing signal bursts when one of a plurality of intercom stations goes off hook and first initiates a call to another of the plurality of intercom stations.
U.S. Pat. No. 4,081,624 issued to Steven Kerman and Fumio Tsutsumi entitled "Key Telephone Intercom System" uses three leads to connect plural telephones and an intercom line control circuit. The leads comprise two walking circuit leads and one control lead, typical of prior art multi-wire exchange systems. Exclusion circuits in each of the telephones are controlled by signals applied on a single control lead to: (1) allow a telephone to seize the intercom line circuit when it is in an idle state; (2) allow the called telephone (which signal is via a separate pair of calling leads) to answer without being excluded; and (3) exclude all other telephones from the intercom line circuit after the calling telephone has seized the intercom line circuit.
In U.S. Pat. No. 4,088,846 issued to James R. McEowen there is provided a "hold-plus-intercom for single-line stations." This multi-wire system is for single line customers and utilizes existing non-key telephone sets and four conductor wiring planned together with an additional adjunct unit per telephone instrument and a common control unit. Hold, broadcast intercom, and their associated visual signals are controlled by each adjunct unit which is interposed between the associated telephone set and the four conductor cable.
Another recent patent is U.S. Pat. No. 4,107,473 issued to Ben Pierce and entitled "Two Way Paging System Transmission Direction Sensing and Control Apparatus and Method." In the Pierce patent, a paging system is entered through appropriate telephone equipment at a master station to supply an audio paging output at a remote station. A paging amplifier is connected to drive a speaker at the remote station to provide the audio output. A direction sensing circuit is disposed between the master and remote stations which operates to sense time relationship between two signals appearing at two separate points within the direction sensing circuit. One time relationship between the two signals indicates a master station transmission and control, and another time relationship indicates a remote station transmission.
In U.S. Pat. No. 1,899,084 issued to George R. Eaton and Glen Kiner, there is provided a telephone system relating to automatic telephone systems of the two-wire type. The Eaton-Kiner patent is directed to older telephones of the rotary dial type.
Two recently issued patents having Harry R. Rasmussen as inventor on the first (U.S. Pat. No. 4,132,860) and Harry R. Rasmussen and Gene Kimzey and Robert Hailey as inventors on the second (U.S. Pat. No. 4,133,985) are both directed to key telephone systems. U.S. Pat. No. 4,132,860 provides a "hold" control for a key telephone system which is primarily directed to a two line system that is particularly tailored for customers needing less than five telephone lines from a central office. The key telephone system in the '985 patent utilizes visual indicator lights and manual control buttons for each telephone instrument along with the control circuitry. Visual indicator lights and manual control buttons for each telephone are packaged in a small compact unit that is readily attachable to an existing standard telephone instrument of the type intended for single line use.
These prior art systems suffer in that they do not provide all of the desirable signalling, intercom, and paging functions desirable to a complete telephone system which system employs only two wires in the exchange.
Thus, it is an object of the present invention to provide a two wire exchange system providing a plurality of desirable signalling, intercom and paging functions.
It is an object of the present invention to provide a two wire exchange system which provides means for monitoring and detecting a tone signalling system in which a tone which may be a dual tone multifrequency tone or a single tone for rotary dial telephones, is generated on the line at the local telephone instrument and the subsequent activation of a relay which places a calling party on hold.
It is another object of the present invention to provide a release hold capability which allows a party on hold to be easily and quickly reconnected to the answering telephone instrument line by the depressing of a tone signal generating key buttons.
It is another object of the present invention to provide a two wire exchange system for telephones in which any one of the plurality of common connected telephones in the system can be used by the recipient of a call to quickly receive an incoming call by the depression of a tone signal generating key button.
It is another object of the present invention to provide a tone remainder for use with two wire exchange systems in which calls on hold which are not picked up will automatically generate a warning tone at desired intervals until the recipient of the call reconnects with the caller placed on hold.
It is another object of the present invention to provide a "screen call" function which answers calls and places them on hold responsive to the depression of a tone signal generating key button.
It is another object of the present invention to provide an in-house intercom and paging system for use with the two wire exchange system, and a release from paging and in-house intercom function associated therewith.